Transducers



Jan. 21, 1958- I... J. BOBB ET AL TRANSDUCERS Filed Aug. 29,1956

2 Sheets-Sheet 1 IN VEN TOR! ll 0? J. 505.5

' Jan. 21, 1958 1.. J. BOBB, ETAL TRANSDUCERS 2 Sheets-Sheet 2 Filed Aug. 29, 1956 INVENTORS .Ua e States TRANSDUCERS Lloyd J. Bobb, Glenside, Pa., andCharles A. Perry, Cleveland, Ohio, assignors to Philco Corporation, Philadelphia, Pa., a corporation of Pennsylvania Application August 29, 1956, Serial No. 606,819 16 Claims. (Cl. 181-32) This invention has to do with electro-acoustical transducers, particularly of the motor driven loud-speaker type, such as the so-called dynamic speaker. The invention is an improvement over that of Lloyd J. Bobb disclosed in his application Serial No. 604,377, filed on August 16, 1956, entitled Transducers and assigned to the same assignee as the present invention.

The invention of Lloyd J. Bobb was based on the discovery that certain acoustical advantages can be achieved by the use of a motor-driven loud-speaker diaphragm which has a characteristic size and form, somewhat similar to that of a miniature boat. The surface of such a diaphragm is concave in one direction and is quite narrow-not wider than about three inches but usually at least as wide as about one inchwhile being very elongated, being at least about five times and often up to about seven times as long as wide. i The present invention, briefly stated, improves the aforementioned, narrow and elongated diaphragm, mainly with respect to the frequency range and response obtained in the use thereof, by shaping the diaphragm in a novel and special way. The new and preferred diaphragm form is cylindro-segmental and is specifically based on a certain combination of fiat cylinder wedges. This will be described in greater detail hereinafter, with reference to the drawing appended hereto, wherein Figures 1 and 2 are front and side views, respectively, or a preferred embodiment of the new diaphragm.

Figures 3, 4 and are sections taken respectively along lines 33, 4-4- and 55 in Figure 2.

Figure 6 shows a modification of the section of Figure 5.

Figures 7 and'S are front and side views, respectively, of a loud-speaker comprising the new diaphragm, and

Figure 9 shows a modification of Figure 7.

Referring to Figures 1 and 2, the new device is shown as comprising an elongated, narrow, approximately boatshaped diaphragm body 10, substantially of cylin'drosegmental shape. The concave side of this shape is preferably used as the front or mouth of the speaker.

With greater particularity in a geometrical sense, the preferred new shape is formed of two flat cylinder wedges or ungulae 11, 12, merging at a blunt or obtuse angle. The form of each ungula or longitudinal one-half of the diaphragm can best be visualized when noting the broken line 11-C in Figure 2, which completes the side view projection of the complete cylinder of wedge 11, having axis 11-A. This may be a right circular cylinder. The second cylinder wedge 12 has the same form and has an axis 12-A, intersecting the first-mentioned axis 11-A at a point 13 on the acoustical loud-speaker axis 13-A. The two cylinder axes intersect the acoustical axis at equal angles which are somewhat less than ninety degrees on the concave side of the diaphragm. 1he: two cylinder wedges 11, 12 have a common base from which they and it will be understood that this base is a short, more or less circular ellipse when the form of the cylinders, as noted above, is right circular. Referring further to .the surfaces which truncate the two diverging ungulae and form the front edges: these surfaces preferably lie in a single plane which intersects the aforementioned common base and axis 13-A at right angles and wherein the two ungulae overlap.

A collar 14, substantially extending along the over lapping front edges of the two cylindro-segmental parts or ungulae, is secured to these edges and surrounds the entire front or mouth of the diaphragm. Corrugations 15 of the usual cross-sectional shape are formed in the collar. Opposite the corrugated collar and around the aforementioned common base of the two cylinder wedges, a relatively small, cylindrical neck 16 is provided for connecting the diaphragm to a voice coil or the like. This neck may extend a short distance rearwardly, coaxially with the speaker axis 13-A. We either may or may not install a suitably formed dust cap 17, covering this neck 16. For obtaining the best performance, it is important that the transition from the neck 16 to the cylinder wedges 11, 12 be formed as a smoothly curved surface 18..

only when the cylindro-segmental form is used in combination with the features of narrowness and elongation, as referred to.

It has been found desirable to use practically identicalcylinder radii R in the longitudinally successive crosssections 3-3, 4-4, and 5-5 of each arm of the diaphragm, so that all of said cross-sections, as shown in Figures 3 to 5, have flat segmental forms, like those of tapering U-shaped channels, differing. from one another only in the rise of the diaphragm segment over the plane of collar 14. It has further been found advantageous to make this radius R about equal to the height of the diaphragm, excluding the collar, at the central cross-section.

55 traversing the neck 16, and to definitely reduce this rise, but only to about one-third of said radius, adjacent each end 19.

bining the cylindro-segmental curvature with at least a blunt angularity between the two cylinder axes, and yet to utilize a longitudinal reinforcing effect, provided by the cylindro-segmental design. While we do not wish to be bound to any theory or explanation, it may be considered that the described curvature of the diaphragm is of assistance in enabling different surface portions to vibrate at all sonic frequencies and that said reinforcing tends to extend the area which vibrates, mainly at high frequencies.

The radii T of the smooth transition surfaces 18, as best shown in Figure 5, may often be fairly small, without loss of acoustical quality or power, particularly when the diaphragm is made very narrow. The proportions,

of Figure 5 are based onthe use of a standardvoice coil It seems to be acoustically" important at least to approach a three-dirnensional curvature, by comtogether with a diaphragm of a width W of about one inch and a half. Figure 6, on the other hand, shows a corresponding, central, sectional view of a relatively large diaphragm in accordance with this invention, which may have a width W] of about two and a half inches. The size and form of the voice coil, and correspondingly that of the neck 16, may be the same in this case as in Figure 5, the power and other characteristics of a standard coil being adequate for either size of the present type of diaphragm; but in view of the use of cylinder wedges having a largerradius R-l, there is used a correspondingly larger radius T-1 of the transition surface 18-1.

Returning to Figure 1: it has been found advantageous to form the ends 19 of the diaphragm in a rounded-off and particularly a smoothly, semicircularly rounded-off form. correspondingly, the collar 14 may best be provided with terminal portions 20 and corrugations 21 in the approximate forms of semi-circular arcuate rings, whereas the lateral and major course of the collar and corrugations, between these ends, may follow a very flat elliptical curve, in view of the slightly oblique cutting off of the cylinder segments. Thus the rounded end portions 19 lie in the principal plane of the corrugated collar 14, that is, in the chordal plane of the cylindro-segmental diaphragm 11, 12; each end portion 19 having an approximately semi-circular outline in said plane, at the inner edge of the terminal portion and corrugation 20, 21.

Referring next to Figures 7 and 8: the outermost part or rim of collar 14 may be clamped in or under a flange structure 22; and a suitable housing or bridge structure 23 having apertures 23a may connect this flange with the acoustical motor or voice coil unit 24. The details of this unit need not be explained herein; the coil, of course, is suitably secured to the neck 16 of the diaphragm. As usual, an acoustically transparent cover, fragmentarily shown at 25, may extend across the mouth of the speaker; it may be formed for instance of a sheet of fabric and/ or a system of fret work. Four fasteners 26 may be convenie'ntly located in the four corners of a rectangular flange 22 for the rounded-01f, elongated diaphragm; they may be used to secure the speaker to a panel, not shown.

In the modification of Figure 9, the flange structure 22 additionally provided with two terminal, transverse b'afile means 27, each extending across one end portion of the mouth of the speaker and covering about one-third of the length of the corresponding, rounded-off cylinder wedge. By this simple battling means the range of flat frequency response of the speaker is additionally extended without objectionable elfect upon the directional pattern, the sound output power and other results. No such improvement is obtained by simply making the diaphragm correspondingly shorter; nor is it possible to obtain results of equal kind or quality when providing the speaker with bafiles of previously known types, such as peripherally arranged or longitudinally slotted baflles.

In operation, the new loud-speaker can be used for a variety of purposes, such as reproducing speech or music or both. For instance, a speaker according to Figure 9 was found to be able to handle successfully not only he qu'encies of speech, reaching from about 100 to well over 5,000 cycles, but also the frequencies of music, reaching from about 30 to at least about 12,000 cycles. When only speech is reproduced, it was found that the width of the new diaphragm may desirably range up to about three inches, to insure broad distribution of the sound, and down to no less than about one inch, to avoid loss of power in the lower frequencies. When music is additionally or exclusively reproduced, it was found that the maximum as well as the minimum width of the diaphragm may best be close to one inch, to secure adequate repro-.

duction and diffusion of all sounds. One inch, of course, is the approximate wavelength of relatively high harmonies of musical notes or overtones of musical instruments, and is less than one half of the full wavelength of the highest fundamental notes.

Byvirtue of features including mainly this narrowness in combination with the cylindro-segmental design of the diaphragm, the new speake'f is improved both as to sensitivity and accuracy of sound reproduction, while being very efficient as to directional pattern, frequency range, power output and other features of performance. The new speaker has provided a frequency response curve with a practically smooth rise from 27 to cycles, with a substantially flat course from 100 to 5,000 cycles, and with a fairly smooth fall from 5,000 to 20,000 cycles; and substantially throughout this Wide range, broad diffusion and high sensitivity have been achieved, with normal wattages of voice coil input and with very acceptable characteristics in all other respects. Even very high audible sounds, such as the highest overtones of violins, organs, etc., are widely diffused; At the same time even the lowest bass voices as well as all intermediate sounds are very adequately and distinctly reproduced and distributed. No previous speaker unit is known to be capable of any such or nearly comparable performance.

While only a single embodiment of the invention has been described, it should be understood that the details thereof are not to be construed as limitative of the invention, except insofar as set forth in the following claims.

We claim: p

l. A transducer diaphragm of substantially cylindrosegmental shape, having rounded end portions lying in the chordal plane of the cylindro-segmental diaphragm, each end portion having approximately semi-circular outline, in said plane.

2. A loud-speaker diaphragm of narrow elongated shape substantially in the form of a pair of cylindrosegmental surfaces merging with one another at a blunt angle.

3. A diaphragm as described in claim 2, wherein said surfaces have identical forms and symmetrical arrangement.

4. A diaphragm as described in claim 2, wherein said surfaces are truncated by a common plane, opposite said blunt angle.

5. A diaphragm as described in claim 4, wherein the truncated plane containing the axes of the cylindrosegmental surfaces.

6. A diaphragm as described in claim 4, wherein the truncating plane intefsects the two cylindro-segmental branch surfaces at uniform angles.

7. A diaphragm as described in claim 2 additionally comprising a collar forming an integral, marginal part of said surfaces and having two elongated, slightly curved, elliptical sides.

8. A diaphragm as described in claim 7, wherein said surfaces and said collar are semi-circularly rounded at their ends.

9. A loud-speaker comprising a diaphragm of elongated, substantially cylindro-segmental shape and a pair of bafiies', each extending across a terminal part of the mouth of the diaphragm.

10. A loud-speaker as described in claim 9, wherein said baflies cover substantially one-third of the mouth of the elongated diaphragm.

11. A loud-speaker of substantially cylindr'o-segmcntal shape no wider than about one to three inches, substan-' tially longer than wide, and wherein said shape is formed of a pair of cylinder wedges the axes of which intersect one another at a blunt angle.

12. In an electro-a'coustical transducer, a diaphragm body having the approximate shape of a pair of cylinder wedge surfaces diverging from a common base and truncated by a single plane; said pair of surfaces being narrow across their axes and elongated along the same.

13. In a transducer as described in claim 12, a dia phragm collar surrounding the diaphragm body, and an electrical unit centrally connected with the diaphragm body.

14. In a dynamic speaker, a diaphragm having a sur face in the form of a small boat with central, approxi mately semi-circular cross-section, and wherein outer cross-sections of the diaphragm are approximately circular angle, for attaching to said neck an electro-acoustica1 arcs of approximately uniform radius and outwardly demotor adapted to move the diaphragm in directions bicreasing 'hei-ght. seating said angle.

15. A sound reproducer diaphragm of narrow, elongated shape, no wider than about one to three inches, said 5 References Cited in the file 0f thls Patent diaphragm being form-ed by a pair of mutually merging, UNITED STATES AT T substantially cylindro-segmental surfaces, the axes of which 1,930,328 Tichenor et a1 Oct 10, 1933 lntersect at a blunt angle.

16. A diaphragm as described in claim 15 having a FOREIGN PATENTS central, hollow neck in the region of the apex of said 10 332,995 Great Britain Aug. 7, 1930 PATENT OFFICE CERTIFICATE OF CORRECTION Patent Noa 2,820,527 January 21, 1958 Lloyd J, Bo'bb e1; ale

Column 1, line 42, for "or a" read w of a column 4; line 41, for "truncated plane" read trunc ating plane is normal to the plane Signed and sealed this 25th day of March 1958.,

(SEAL) KARL no AXLINE ROBERT C. WATSON Attesting Officer issioner of Patents U. S. DEPARTMENT OF COMMERCE PATENT OFFICE CERTIFICATE OF CORRECTION Patent Noa 2,820,527 January 21, 1958 Lloyd J. Bobb et ale It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 1, line 42, for or a" read of a column 4, line 41, for truncated plane" read truncating plane is normal to the plane Signed and sealed this 25th day of March 1958.

(SEAL) Attest:

KARL HO AXLINE ROBERT C. WATSON Attesting Officer (omissioner of Patents 

